package string;

public class CharAtDemo {
    public static void main(String[] args) {
//        String str="thinking in the java";
//        char c=str.charAt(2);
//        System.out.println(c+",");
        String aa="1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        String sum="";
        int a;
        for(int i=0;i<4;i++){
        a=(int)(Math.random()*(aa.length()));
        sum=sum+aa.charAt(a);
        }
        System.out.println(sum);

    }
}
